1. Field of the Invention
The invention relates to a position detecting switch that detects at which selected position out of predetermined selected positions an object whose position is to be detected is located and outputs the detected result as an analog signal.
2. Description of the Related Art
In an apparatus having a drive mechanism incorporated therein such as a video apparatus and a copying machine, a diversity of switches are employed to detect the position of a driving object. For example, for detecting the rotating angular position of a driving object, a rotary switch is often used.
FIG. 4 is a circuit diagram of a 4-bit output rotary switch with a relationship between the predetermined rotating angular positions of a rotor (not shown) and the corresponding outputs thereof shown together. In FIG. 4, reference numeral 2 designates a brush serving as a movable contact that is coupled to the rotor; 3 to 5, switch patterns serving as fixed contacts formed on a not shown board in annular form; 6, a pull-up resistor; 7, an input terminal for inputting a power supply voltage (5 V); and 8, an output terminal for outputting 4-bit data (A, B, C, D).
Numerals 1 to 11 given at the bottommost position in FIG. 4 designate the predetermined rotating angular positions of the rotor. For example, when data to be outputted from the output terminal 8 is (1, 1, 1, 1), it is meant that the brush 2 is located at the rotating angular position 1. When data is changed to (0, 1, 1, 1), it is meant that the brush 2 has moved to the rotating angular position 2 by rotation of the rotor.
Thus, which rotating angular position 1 through 11 the rotor is currently located at can be identified by checking the content of data outputted from the output terminal 8. As a result, the rotating angular position of the driving object coupled to the rotor can be detected.
However, in the case of the aforementioned conventional example, when the rotary switch must be connected to an analog input port of a microcomputer, a D/A converter must be interposed therebetween, which imposes a problem in terms of promoting cost reduction.
A simple modification of a rotary encoder into an analog output type does not give a decisive solution to the problem, because inexpensive circuit parts such as pull-up resistors cannot be used, so that the number of parts is increased and so is the number of wiring points. When a wide voltage range is required in particular, many expensive circuit parts must be employed, which imposes the problem of an increased cost. It may be noted that such problem of increased cost will be described in detail with reference to FIG. 2 later.
This problem is not specific to rotational movement type position detecting switches such as rotary switches, but the same problem is addressed for linear movement type position detecting switches as well.